(1) Field of the Invention
The invention of the present application relates to a main bearing for supporting a crankshaft of an internal combustion engine.
(2) Description of the Related Art
A crankshaft of an internal combustion engine is supported at a journal section thereof by a cylinder block lower part of the internal combustion engine via a main bearing made of a pair of half bearings. For the main bearing, a lubricating oil that is discharged by an oil pump is fed into a lubricating oil groove that is formed along an inner circumferential surface of the main bearing through a through-port that is formed in a wall of the main bearing from an oil gallery that is formed in a cylinder block wall. Further, a first lubricating oil path is formed by being penetrated in a diameter direction of the journal section, and both end openings of the first lubricating oil path communicate with the lubricating oil groove of the main bearing. Furthermore, a second lubricating oil path passing through a crank arm section is formed by branching from the first lubricating oil path in the journal section, and the second lubricating oil path communicates with a third lubricating oil path that is formed by being penetrated in a diameter direction of a crankpin. In this manner, the lubricating oil which is fed into the lubricating oil groove formed on the inner circumferential surface of the main bearing through the through-port from the oil gallery in the cylinder block wall passes through the first lubricating oil path, the second lubricating oil path and the third lubricating oil path, and is supplied between a sliding surface of the crankpin and a connecting rod bearing from a discharge port that is opened in a terminal end of the third lubricating oil path (for example, see JP-A-8-277831).
The lubricating oil which is fed to the lubricating oil groove of the main bearing from the oil gallery in the cylinder block wall is likely to be accompanied by residual foreign matters that are generated at a time of machining of respective components, for example. The foreign matters are likely to damage sliding surfaces between the journal section and the main bearing and sliding surfaces between the crankpin and the connecting rod bearing, and therefore, need to be discharged to an outside quickly from the flow of the lubricating oil.
Consequently, there has been conventionally provided a main bearing for supporting a crankshaft of an internal combustion engine, wherein an inner circumferential surface of each of semi-cylindrical bearings that configure the main bearing is formed of two kinds of circular arcs with different curvatures, namely, a first curved surface (a main cylinder portion) including a circumferential central portion and a second curved surface (a crush relief portion), an axial groove is formed through an entire length in a width direction of both butting end surfaces of the semi-cylindrical bearings, the second curved surface is formed in a range of 20° to 50° as a circumferential angle (θ) measured from a circumferential end surface of each of the semi-cylindrical bearings, and a number of fine circumferential grooves are formed in the second curved surface (FIGS. 1 and 5 of JP-A-2011-58568), so that foreign matters that accompany the lubricating oil and enter a lubricating oil groove of one of the semi-cylindrical bearings are fed to and dispersed in a gap formed by the second curved surface and a surface of the crankshaft, are thereafter discharged to an outside of the main bearing from the axial groove, and are prevented from reaching an inner circumferential surface position of the other semi-cylindrical bearing and being locally embedded and accumulated in the same inner circumferential surface (paragraph 0011 of JP-A-2011-58568).